Incorrect type inference for Record with symbol key

TypeScript Version: Nightly

Search Terms: Record, Symbol, symbol as index

Code

export type SN = Record<symbol, number>

const s = Symbol()
const sn: SN = {}

const n = sn[s] // n is of type any instead of number

Expected behavior:

A Record with symbols as key should allow to access properties by symbol with correct type

Actual behavior:

All keys are any type.

Playground Link: http://www.typescriptlang.org/play/?noImplicitAny=false&strictNullChecks=false&strictFunctionTypes=false&strictPropertyInitialization=false&strictBindCallApply=false&noImplicitThis=false&noImplicitReturns=false&alwaysStrict=false&ts=3.9.0-dev.20200308#code/KYDwDg9gTgLgBDAnmYcDKA5OBeOAlYAY2gBMAeAZ0QFsAjCAGwBo4A7AVzuCgD4AoPsVYV4FHOhr0GACgCUgiMNGsAXOiy4A3gF8BQkW3EVWAbQoBdIA

Related Issues: #1863

Reproduce the example in the issue using the TypeScript Nightly playground or the shown TypeScript version, then trace the compiler's handling of indexed access on Record<symbol, number>. Compare the inferred type of sn[s] with the expected number and use the related issue #1863 for context. Done means symbol-keyed Record access is inferred as number rather than any, with a regression test covering the example.